Approximately 7800 spinal cord injuries occur in the United States each year. Motor vehicle accidents are the leading cause of spinal cord injury, followed by acts of violence, falls, and sports. The majority of injuries occur at the mid-cervical and upper thoracic regions of the spinal cord.
Approximately 45% of the injuries result in total or complete loss of sensation and function below the level of injury. The remaining 55% of the injuries result in partial loss of sensation and function below the level of injury. Such injuries are incomplete. In incomplete spinal cord injuries, the primary traumatic injury can destroy as much as 90% of the axons in the spinal cord. However, such patients can still recover substantial function as a result of the axons that are spared at the injury site.
The primary trauma to the spinal cord causes a central hemorrhagic necrosis. The central part of the spinal cord, i.e., the gray matter dies first. Generally a rim of white matter containing myelinated axons is preserved. Following the initial injury, a series of degenerative processes which promote tissue damage beyond the original site of injury are initiated. This is referred to as secondary injury.
At present, the only method which has currently been shown to be effective at reducing or minimizing the damage resulting from this secondary injury is intravenous injection of the glucocorticoid methylprednisolone. Methylprednisolone is a potent free radical scavenger which may also serve to reduce inflammation of the central nervous system. Methylprednisolone is administered to the patient in high doses (30 mg/kg body weight) shortly after injury, typically within the first 8 hours. Unfortunately, prolonged administration of glucocorticoids has adverse systemic effects (e.g. increased incidence of sepsis and pneumonia) and is limited in its therapeutic window.
Accordingly, it is desirable to have additional methods for treating spinal cord injury, particularly the secondary spinal cord injury that results from trauma. A treatment which can be employed at a time which is more than 8 hours after occurrence of the initial injury is especially desirable.